1. Field of the Invention
The present invention relates to a mounting technique for an image decoding device and image encoding device complying to various international standards for moving image compression and expansion. In particular, the present invention relates to an image decoding device and image encoding device which increases resistance to bit error generated in encoded bit streams.
2. Description of the Related Art
The ITU-T (International Telecommunication Union-Telecommunication Sector) Recommendation H.263 is known as a means of encoding and decoding image signals. H.263 divides the encoding and decoding of moving image data into a plurality of hierarchies.
FIG. 1 shows the structure of video data hierarchies in H.263. The layer in an uppermost position is called a picture layer. The picture layer is comprised from a plurality of GOB (Group of Blocks) layers. A macroblock layer exists in a lower layer of the GOB layers and a block layer exists in a lower layer of the macroblock layer.
FIG. 2 shows the structure of a macroblock. One macroblock is comprised of six blocks (8 pixelsxc3x978 lines) with block numbers 1xcx9c6 as shown in FIG. 2. Block numbers 1xcx9c4 are blocks for luminance components. Block numbers 5, 6 are color difference component blocks.
FIG. 3 shows an example of a conventional encoded bit stream. Binary digit strings which are respectively called picture start codes (PSC), and GOB start codes (GBSC) are added to the header of picture layer information and GOB layer information. These start codes (SC) are unique words (bit streams with only one interpretation) and have the function of showing the start of picture layer information and GOB layer information.
A GOB number or the like which is a number of the relevant GOB is contained in the GOB layer information. Layer information such as quantization step size, encoded mode which shows intra-encoded or inter-encoded is contained in the macro block (MB) layer information. Thereafter the block data information is stored.
Intra-encoded is an encoded mode which encodes only picture data itself of encoded images without using other pictures. Inter-encoded is an encoded mode which encodes picture information of encoded images using information of other pictures with a time frame.
FIG. 4 is a block diagram showing the structure of a conventional image decoding device using H.263. An encoded bit stream which is encoded is input into a syntax analysis section 1. Each layer of information of picture layer, GOB layer and macroblock layer is analyzed and decoded on the basis of the H.263 syntax. Thus block data information is analyzed.
At this time, when layer information and block data information not matching a fixed syntax is analyzed, an error syntax detection signal 1e to that effect is output to the error processor 7. The obtained quantization step size 1d is output to a reverse quantization processor 5 and the encoded mode 1b is output to a reverse DCT/decoding image generator 6.
When analyzed block data information is information determined by the H.263 decoding method, the syntax analysis section 1 determines that errors are not contained in the input encoded bit stream due to the influence of errors contained in an encoded bit stream even if the block data information to be analyzed is different block data information. Thus a quantization index column 1a for a decoded block unit is output to the reverse quantization processor 5. The quantization index column 1a is comprised of columns of quantization indexes. A quantization index is a quantization DCT coefficient.
A reverse quantization process applied to the quantization index column 1a of the block unit is provided in the reverse quantization processor 5 using a quantization step size Id input from the syntax analysis section 1. A DCT coefficient column 1f of a block unit is output to the reverse DCT/decoding image generator 6.
A reverse DCT process is provided with respect to the DCT coefficient column 1f of the block unit in the reverse DCT/decoding generator 6, a decoded image is generated based on the input encoded mode 1b and the generated decoded image is output.
The error processor 7 generates and outputs a decoded image by error suppression based on a fixed method on receipt of an error syntax detection signal 1e which shows layer information or block data information from the syntax analysis section 1 which does not match a fixed syntax.
However in a conventional image signal decoding device as shown above, the problem has arisen that error detection can not be performed since the image decoding device analyzes and performs decoding without recognizing the generation of errors in the encoded bit stream. This is the result of the block data information being block data information which is adapted to a fixed syntax which is predetermined on the encoded and decoded sides such as in the case of an H.263 video method or the like. This is the case even if the block data information which is different from the block data information which is to be analyzed is analyzed by an encoded bit stream due to the influence of errors contained in the encoded bit stream.
The present invention is proposed to solve the above problems and has the object of providing an image decoding device which can perform error detection even when block data information is adapted to a fixed syntax and such block data information, which differs from the block data information which should be analyzed, is analyzed by encoded bit stream.
The invention has a further object of obtaining an image encoding device generating an encoded bit stream which can effectively detect errors contained in an encoded bit stream in the image decoding device.
An image decoding device according to claim 1, which receives a signal containing image compression data through a transmission circuit and performs an expansion process with respect to image compression data, comprises a monitoring means which receives compression data, monitors the state of the transmission circuit and outputs a control signal to control an error block detection means based on a monitor result, and an error block detection means which determines whether an error is contained in received image data and which outputs an error detection state in image data. The error block detection means controls the sensitivity of error detection based on a control signal output from the monitoring means.
In such a way, under good reception conditions it is possible to avoid error detection due to the error block detection means and thus it is possible to perform overall stable decoding operations.
An image decoding device according to claim 2 performs image expansion processing and reverse orthogonal conversion on fixed block units with respect to image compression data. The image decoding device comprises an error block detection means which receives a threshold value and image signal in a frequency domain, determines whether or not a block data error is contained therein based on the threshold value and the image signal in a frequency domain and outputs an error detection state in block data.
In such a way, it is possible to detect even error blocks adapted to a fixed syntax and it is possible to generate a decoded image with little influence of errors contained in encoded bit streams.
An image encoding device according to claim 3 divides image data into block units, performs orthogonal conversion and performs compression coding on each block unit. The image encoding device comprises an encoded data value limiting means which receives a threshold value and an image signal in a frequency domain and which outputs an image signal with an added limit in a frequency domain based on a predetermined threshold value and an image signal in a frequency domain.
In such a way, it is possible to perform efficient detection of errors contained in encoded bit streams in the image decoding device. It is possible to generate an encoded bit stream which can generate a decoded image with little influence of errors contained in encoded bit streams.
An image decoding device according to claim 4 is characterized in that the error block detection means receives a threshold value defining a range of values of an image signal value in a frequency domain and an image signal in a frequency domain. The error block detection means performs error detection on block data based on whether an image signal value in a frequency domain is contained in the range of values or not and outputs an error detection state.
In such a way, it is possible to detect error blocks matching a fixed syntax and it is possible to generate a decoded image with little influence of errors contained in encoded bit streams.
An image decoding device according to claim 5 is characterized in that the error block detection means receives a threshold value variably defining a range of values of an image signal value in a frequency domain, which performs error detection on block data based on whether an image signal value in a frequency domain is contained in the range of variable values and which outputs an error detection state.
In such a way, it is possible to detect error blocks matching a fixed syntax and it is possible to generate a decoded image with little influence of errors contained in encoded bit streams.
An image encoding device according to claim 6 is characterized in that the encoded data value limiting means receives a threshold value defining a range of values of image signal values in a frequency domain and an image signal in a frequency domain. The encoded data value limiting means replaces an image signal value in the converted frequency domain with a value contained in the range of values based on whether an image signal value in the converted frequency domain is contained in the range of values and outputs encoded data.
In such a way, it is possible to perform effective detection of errors contained in an encoded bit stream in the image decoding device and it is possible to generate an encoded bit stream which can generate a decoded image with little influence of errors contained in encoded bit streams.
An image encoding device according to claim 7 is characterized in that the encoded data value limiting means receives a threshold value variably defining a range of values of an image signal value in a frequency domain and an image signal in a frequency domain. The encoded data value limiting means replaces an image signal value in the converted frequency domain to a value contained in the range of values based on whether an image signal value in the converted frequency domain is contained in the range of values and outputs encoded data.
In such a way, it is possible to perform effective detection of errors contained in an encoded bit stream in the image decoding device and it is possible to generate an encoded bit stream which can generate a decoded image with little influence of errors contained in encoded bit streams.
An image decoding device according to claim 8 is characterized in that the error block detection means receives a threshold value defining a range of frequencies of an image signal list in a frequency domain and an image signal in a frequency domain, and performs error detection in block data and outputs an error detection state based on whether or not a non-zero coefficient which corresponds to the highest frequency component of the coefficients contained in the image signal list in the frequency domains is contained in the frequency range given by the threshold value.
In such a way, it is possible to perform effective detection of errors contained in an encoded bit stream in the image decoding device and it is possible to generate a decoded image with little influence of errors contained in encoded bit streams.
An image decoding device according to claim 9 is characterized in that the error block detection means receives a threshold value variably defining a range of frequencies of an image signal list in a frequency domain, and performs error detection in block data and outputs an error detection state based on whether or not a non-zero coefficient which corresponds to the highest frequency component of the coefficients contained in the image signal list in the frequency domains is contained in the variable frequency range given by the threshold value.
In such a way, it is possible to perform effective detection of an error block matching a fixed syntax and it is possible to generate a decoded image with little influence of errors contained in encoded bit streams.
An image encoding device according to claim 10 is characterized in that the encoded data value limiting means receives a threshold value defining a range of frequencies of an image signal list in a frequency domain and an image signal in a frequency domain, and outputs encoded data which makes coefficient values, which correspond to frequencies above the threshold value, take a value of zero based on whether or not a non-zero coefficient which corresponds to the highest frequency component of the coefficients contained in the image signal list in the frequency domains is contained in the frequency range given by the threshold value.
In such a way, it is possible to perform effective detection of errors contained in an encoded bit stream in the image decoding device and it is possible to generate an encoded bit stream which can generate a decoded image with little influence of errors contained in encoded bit streams.
An image encoding device according to claim 11 is characterized in that the encoded data value limiting means receives a threshold value variably defining a range of frequencies of an image signal list in a frequency domain and an image signal in a frequency domain, and outputs encoded data which makes coefficient values, which correspond to frequencies above the threshold value, take a value of zero based on whether or not a non-zero coefficient which corresponds to the highest frequency component of the coefficients contained in the image signal list in the frequency domains is contained in the frequency range variably given by the threshold value.
In such a way, it is possible to perform effective detection of errors contained in an encoded bit stream in the image decoding device and it is possible to generate an encoded bit stream which can generate a decoded image with little influence of errors contained in the encoded bit stream.
An image decoding device according to claim 12 is characterized in that a block column detection means is provided which is given an error detection state output by the error block detection means, which counts the number of blocks determined to contain errors in the block data of the error detection states by a block column unit which is comprised by a plurality of blocks, which performs error detection of data in block columns based on that count number and a preset threshold value and which outputs an error detection state of data in block columns.
In such a way, it is possible to suppress the possibility of performing error determination which determines that an error is contained in a block which does not actually contain an error. Furthermore it is possible to generate a decoded bit image with little influence of errors contained in the encoded bit stream.
An image encoding device according to claim 13 is provided with a multiplexing means which receives threshold value control information which updates the threshold value and which multiplexes and outputs such threshold value control information to the encoded bit stream.
In such a way, it is possible to perform effective detection of errors contained in an encoded bit stream in the image decoding device and it is possible to generate an encoded bit stream which can generate an decoded image with little influence of errors contained in the encoded bit stream.
An image decoding device according to claim 14 is provided with an analyzing means which decodes and analyzes threshold value control information with an input encoded bit stream. An error block detection means inputs threshold value control information decoded and analyzed in the analyzing means, updates the threshold value based on the threshold value control information and performs error detection in the block data and outputs an error detection state based on the updated threshold value and the image signal in the frequency domain.
In such a way, it is possible to perform detection of an error block matching a fixed syntax and it is possible to generate an encoded bit stream with little influence of errors contained in encoded bit streams.
An image encoding device according to claim 15 is characterized in that a multiplexing means is provided which receives threshold value information used when the encoded data value limiting means limits the image signal distribution in the frequency domain and which multiplexes and outputs such threshold value information to the encoded bit stream. The encoded data value control means outputs encoded data in which the image signal distribution in the frequency domain is limited based on the threshold value information.
In such a way, it is possible to perform effective detection of errors contained in an encoded bit stream in the image decoding device and it is possible to generate an encoded bit stream which can generate an decoded image with little influence of errors contained in the encoded bit stream.
An image decoding device according to claim 16 is characterized in that an analyzing means which decodes and analyzes threshold value information used when limiting the image signal distribution in the frequency domain by the encoded bit stream. The error block detection means performs error detection in the block data and outputs an error detection state based on the threshold value information decoded and analyzed by the analyzing means.
In such a way, it is possible to perform detection of an error block matching a fixed syntax and it is possible to generate a decoded image with little influence of errors contained in encoded bit streams.
An image encoding device according to claim 17 is characterized in that a multiplexing means is provided which multiplexes and outputs limiting operation control information showing whether or not the encoded data value limiting means will perform a limiting operation. The encoded data value control means performs a limiting operation based on the limiting operation control information.
In such a way, it is possible to perform effective detection of errors contained in an encoded bit stream in the image decoding device and it is possible to generate an encoded bit stream which can generate an decoded image with little influence of errors contained in the encoded bit stream.
An image decoding device according to claim 18 is characterized in that an analyzing means is provided which analyzes limiting operation control information by the encoded bit stream. The error block detection means performs error detection on the block data and outputs an error detection state based on the limiting operation control information analyzed by the analyzing means.
In such a way, it is possible to perform effective detection of an error block matching a fixed syntax and it is possible to generate a decoded image with little influence of errors contained in encoded bit streams.
An image decoding device according to claim 19 is provided with a monitoring means which monitors the strength of a received signal of encoded data as a transmission state and outputs a threshold value control signal for controlling a threshold value when the error block detection means performs error detection in block data based on a monitoring result. The error block detection means controls a threshold value when performing error block detection based on the threshold value control signal from the monitoring means.
In this way, it is possible to avoid the performance of error detection by the error block detection means when reception conditions are good and thus it is possible to perform overall stable decoding operations.
An image decoding device according to claim 20 is characterized in that the monitoring means monitors the generation of bit errors when receiving an encoded signal as a transmission state and outputs an activation control signal which activates or does not activate the error block detection means based on a bit error generation state.
The error block detection means performs detection operations of error blocks based on the activation control signal from the monitoring means.
In this way, it is possible to avoid the performance of error detection by the error block detection means when reception conditions are good and thus it is possible to perform overall stable decoding operations.
An image decoding device according to claim 21 is provided with a monitoring means which inputs a media packet column detects bit errors in the packet based on error detection encoding added to the packet unit, counts the number of bit errors in a media packet unit, and outputs an activation control signal to activate or not activate the error block detection means or not based on a shift in the count value. The error block detection means performs an error block detection operation based on the activation control signal from the monitoring means.
In this way, it is possible to avoid the performance of error detection by the error block detection means when reception conditions are good and thus it is possible to perform overall stable decoding operations.